drop "MIT License" line from LICENSE

I was importing this crate into Google's source control system. The
automation at Google doesn't like the "MIT License" line at the
beginning of the LICENSE-MIT file. AFAICT, the automation is correct
in thinking that the line is not supposed to be there.

For reference, I've made the same change in gitoxide:
GitoxideLabs/gitoxide#1097

LICENSE

@@ -1,5 +1,3 @@
-MIT License
-
 Copyright (c) 2020 Élie ROUDNINSKI (marmeladema) <xademax@gmail.com>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy